1. Technical Field
The present disclosure relates to a method for estimating the signal-to-noise ratio for packet transmission and reception systems of signals based on M-ary differential phase shift keying (M-DPSK) modulations, for example for systems based on receivers of the non-coherent type with differential demodulator, and an apparatus thereof.
2. Description of the Related Art
In the present communication systems using adaptive modulations for ensuring a certain quality of service (QoS), maximizing the spectral efficiency may be advantageous. The key idea of the adaptive modulation is reacting to the changes of the channel conditions by using strong modulation schemes in the case of bad channel conditions and employing less strong modulation schemes in the case of good channel conditions for increasing the transmission speed. The adaptive modulations may be employed both in single carrier systems and in multiple carrier systems, in both cases a reliable estimation of the channel conditions is needed, for example an estimation of the signal-to-noise ratio (SNR), in order to choose the modulation to be employed.
The apparatuses for estimating the signal-to-noise ratio or SNR estimators may be divided in two categories: “data aided” estimators and “not data aided” estimators i.e., the estimators acting on a known data sequence and those acting on an unknown data sequence. The present data aided SNR estimators applied to non-coherent receivers at the input of a differential demodulator do not allow good estimations of the signal-to-noise ratio to be obtained in the presence of impairments that cause a progressive phase shifting of the received constellation symbols. An example of such impairments is the presence of frequency offsets, between transmitter and receiver, on the carrier frequency. On the other hand, the present data aided SNR estimators applied to non-coherent receivers at the output of a differential demodulator are stronger against those impairments, such as carrier frequency offsets, but more sensitive to the noise.